/*
 * This computer program is the confidential information and proprietary trade
 * secret of Apptonelabs, Inc. Possessions and use of this program must
 * conform strictly to the license agreement between the user and
 * Apptonelabs, Inc., and receipt or possession does not convey any rights
 * to divulge, reproduce, or allow others to use this program without specific
 * written authorization of Apptonelabs, Inc.
 * 
 * Copyright (c) 2012-2015 Apptonelabs, Inc. All Rights Reserved.
 */
package com.apptonelabs.vnc.vphone;

abstract public class InStream {

	// check() ensures there is buffer data for at least one item of size
	// itemSize bytes. Returns the number of items in the buffer (up to a
	// maximum of nItems).

	public final int check(int itemSize, int nItems) throws Exception {
		if (ptr + itemSize * nItems > end) {
			if (ptr + itemSize > end)
				return overrun(itemSize, nItems);

			nItems = (end - ptr) / itemSize;
		}
		return nItems;
	}

	public final void check(int itemSize) throws Exception {
		if (ptr + itemSize > end)
			overrun(itemSize, 1);
	}

	// readU/SN() methods read unsigned and signed N-bit integers.

	public final int readS8() throws Exception {
		check(1);
		return b[ptr++];
	}

	public final int readS16() throws Exception {
		check(2);
		int b0 = b[ptr++];
		int b1 = b[ptr++] & 0xff;
		return b0 << 8 | b1;
	}

	public final int readS32() throws Exception {
		check(4);
		int b0 = b[ptr++];
		int b1 = b[ptr++] & 0xff;
		int b2 = b[ptr++] & 0xff;
		int b3 = b[ptr++] & 0xff;
		return b0 << 24 | b1 << 16 | b2 << 8 | b3;
	}

	public final int readU8() throws Exception {
		return readS8() & 0xff;
	}

	public final int readU16() throws Exception {
		return readS16() & 0xffff;
	}

	public final int readU32() throws Exception {
		return readS32() & 0xffffffff;
	}

	// readString() reads a string - a U32 length followed by the data.

	public final String readString() throws Exception {
		int len = readU32();
		if (len > maxStringLength)
			throw new Exception("InStream max string length exceeded");

		char[] str = new char[len];
		int i = 0;
		while (i < len) {
			int j = i + check(1, len - i);
			while (i < j) {
				str[i++] = (char) b[ptr++];
			}
		}

		return new String(str);
	}

	// maxStringLength protects against allocating a huge buffer. Set it
	// higher if you need longer strings.

	public static int maxStringLength = 65535;

	public final void skip(int bytes) throws Exception {
		while (bytes > 0) {
			int n = check(1, bytes);
			ptr += n;
			bytes -= n;
		}
	}

	// readBytes() reads an exact number of bytes into an array at an offset.

	public void readBytes(byte[] data, int offset, int length) throws Exception {
		int offsetEnd = offset + length;
		while (offset < offsetEnd) {
			int n = check(1, offsetEnd - offset);
			System.arraycopy(b, ptr, data, offset, n);
			ptr += n;
			offset += n;
		}
	}

	// readOpaqueN() reads a quantity "without byte-swapping". Because java has
	// no byte-ordering, we just use big-endian.

	public final int readOpaque8() throws Exception {
		return readU8();
	}

	public final int readOpaque16() throws Exception {
		return readU16();
	}

	public final int readOpaque32() throws Exception {
		return readU32();
	}

	public final int readOpaque24A() throws Exception {
		check(3);
		int b0 = b[ptr++];
		int b1 = b[ptr++];
		int b2 = b[ptr++];
		return b0 << 24 | b1 << 16 | b2 << 8;
	}

	public final int readOpaque24B() throws Exception {
		check(3);
		int b0 = b[ptr++];
		int b1 = b[ptr++];
		int b2 = b[ptr++];
		return b0 << 16 | b1 << 8 | b2;
	}

	// pos() returns the position in the stream.

	abstract public int pos();

	// bytesAvailable() returns true if at least one byte can be read from the
	// stream without blocking. i.e. if false is returned then readU8() would
	// block.

	public boolean bytesAvailable() {
		return end != ptr;
	}

	// getbuf(), getptr(), getend() and setptr() are "dirty" methods which allow
	// you to manipulate the buffer directly. This is useful for a stream which
	// is a wrapper around an underlying stream.

	public final byte[] getbuf() {
		return b;
	}

	public final int getptr() {
		return ptr;
	}

	public final int getend() {
		return end;
	}

	public final void setptr(int p) {
		ptr = p;
	}

	// overrun() is implemented by a derived class to cope with buffer overrun.
	// It ensures there are at least itemSize bytes of buffer data. Returns
	// the number of items in the buffer (up to a maximum of nItems). itemSize
	// is supposed to be "small" (a few bytes).

	abstract protected int overrun(int itemSize, int nItems) throws Exception;

	protected InStream() {
	}

	protected byte[] b;
	protected int ptr;
	protected int end;
}
